1. Field of the Invention
The present invention relates to a pattern inspection apparatus, a pattern inspection method, or a program which causes a computer to execute the method, such as a pattern inspection technique which inspects a pattern defect of an object serving as a target plate used in manufacturing a semiconductor, and an apparatus which inspects a defect of a considerably small pattern of a photomask, a wafer, or a liquid crystal substrate used in manufacturing a semiconductor device or a liquid crystal display (LCD).
2. Related Art
In recent years, with a high integration density and a large capacity of a large-scale integrated circuit (LSI), a circuit line width required for semiconductor devices increasingly narrows. These semiconductor devices are manufactured such that a pattern is exposed and transferred on a wafer by a reduced projection exposure device called a stepper while using an original pattern with a circuit pattern formed thereupon (The original pattern is also called a mask or a reticle. The original pattern will be generally called as a mask hereinafter.) to form a circuit. Therefore, in manufacturing a mask to transfer the fine circuit pattern on a wafer, a pattern drawing device which can draw a fine circuit pattern is utilized. A pattern drawing device may directly draw a pattern circuit on a wafer. An electronic beam drawing device is also described in a reference (for example, see Japanese Patent Application, Publication No. 2002-237445).
Alternatively, in addition to the electronic beam drawing device, a laser beam drawing device which draws a pattern by using a laser beam is under development, and is disclosed in references (for example, see U.S. Pat. No. 5,386,221).
An improvement in yield is essential in manufacturing an LSI which requires a lot of manufacturing cost. However, as represented by a 1-gigabit DRAM (Random Access Memory), the order of a pattern constituting an LSI has been changing from a sub-micron order to a nano order. As one serious factor which decreases a yield, a pattern defect of a mask used when an ultrafine pattern is exposed and transferred on a semiconductor wafer by a photolithography technique is known. In recent years, with a miniaturization of an LSI pattern formed on a semiconductor wafer, a size which must be detected as a pattern defect has also become considerably small. For this reason, a pattern inspection apparatus which inspects a defect of a transfer mask used in manufacturing an LSI must be increased in precision.
On the other hand, with development of multimedia, an LCD (Liquid Crystal Display) has a liquid crystal substrate size of a 500 mm×600 mm or larger, and micropatterning of a TFT (Thin Film Transistor) or the like formed on a liquid crystal substrate advances. Therefore, it is required that a considerably small pattern defect be inspected in a large area. For this reason, development of a pattern inspection apparatus which efficiently inspects a defect of a pattern of a large-area LCD and a photomask used in manufacturing the large-area LCD in a short period of time is urgently required.
In this case, in a conventional pattern inspection apparatus, it is known that an optical image obtained by picking up an image of a pattern formed on a target plate such as a lithography mask or the like at a predetermined magnification by using a magnifying optical system is compared with design data or an optical image obtained by picking up the image of the same pattern on the target plate to perform inspection (for example, see Japanese Patent Application, Publication No. HEI08-76359).
For example, as pattern inspection methods, “die to die inspection” which compares optical image data obtained by picking up images of the same patterns at different places on the same mask and “die to database inspection” which generates design image data based on drawing data (information of a design pattern) obtained by converting CAD data used in drawing a mask pattern into data in an inspection apparatus input format and compares the design image data with optical image data serving as measurement data obtained by picking up the image of a pattern are known. In the inspection methods in the inspection apparatus, a target plate is placed on a stage, and a flux of light scans the target plate as a result of the movement of the stage to perform inspection. The flux of light is irradiated on the target plate from a light source and an illumination optical system. Light transmitted through the target plate or reflected by the target plate is focused on a sensor through an optical system. The image picked by the sensor is transmitted to a comparing circuit as measurement data. In the comparing circuit, after alignment of the images, the measurement data is compared with reference data based on an appropriate algorithm. When the measurement data is different from the reference data, it is determined that a pattern defect is present.
In recent years, the line width of a design pattern narrows, the presence of a micropattern for optical proximity correction (OPC) makes it difficult to match the design image data and the optical image data serving as measurement data, and an object which is not essentially determined as a defect is occasionally determined as a defect (pseudo defect). In contrast to this, when a threshold value for decision is moderated, a defect in a pattern which requires a high dimensional precision cannot be detected. For this reason, it has been required that a drawing pattern be compared and inspected at a plurality of inspection precisions.
When a defect appears in a target plate, a user generally reviews the defect. However, a considerably larger number of micropatterns and the like for the above optical proximity correction (OPC) are arranged (for example, at several ten thousands). For this reason, if all the micropatterns are determined as defects, quantity of work and time required to review the defects by a user exceed their limitations. As described above, when a large number of pseudo defects appear in the target plate, the inspection itself must be disadvantageously performed again. Alternatively, an expensive target plate itself must be disadvantageously manufactured again. In contrast to this, when the threshold value for decision is moderated, it is disadvantageously impossible to detect a defect in a pattern which requires a high dimensional precision.
A technique in which drawing patterns are compared and inspected while being classified into a plurality of ranks is disclosed in references (for example, see Japanese Patent Application, Publication No. 2004-191957). However, in this reference, a method of embodying an apparatus by classifying drawing patterns into a plurality of ranks is not concretely described. The method is practically insufficient, and a method for solving the problem is desired. In addition, a method for automatically detecting an OPC pattern from design image data (image data) to reduce the number of pseudo defects is proposed (for example, Japanese Patent No. 3413110).